1. Technical Field
The present invention relates to a method and system for managing mass storage device configuration records in general, and in particular to a method and system for updating mass storage device configuration records during a configuration change within a computer system. Still more particularly, the present invention relates to a method and system for updating mass storage device configuration records during a configuration change within a computer system when not all members of a configured set are present or operational.
2. Description of the Prior Art
A computer system often distributes its logically contiguous data, e.g. a file, across various separate and non-contiguous auxiliary mass storage devices such as magnetic disks. While some systems require a system operator to manage their data distributions, other systems can perform such data distribution automatically. The automatic data distribution and management techniques became well-known through the System/38 and AS/400 mini-computers manufactured by International Business Machine Corp., contributing to their "ease-of-use" reputations. Similar data distribution and management functions are now available on computer systems from a variety of vendors.
There are several different reasons for data distribution within a computer system, including capacity considerations which arise when an entire file cannot fit on a single disk and performance considerations which arise when multiple users require access to different parts of the file simultaneously. Regardless of the reason, however, when logically contiguous data are distributed across multiple auxiliary mass storage devices, the computer system must ensure that all the mass storage devices being used as a set belong to the same set. If they do not, then the logically contiguous data that the mass storage devices are believed to contain will be corrupted. This is true for all types of storage devices, such as magnetic tape, magnetic disk, CD-ROM or a yet to be developed media, that comprise the set.
For a set of mass storage devices to be reliable and fully operational, the computer system must guarantee (1) all the devices within the set are present, and (2) each device can be verified as belonging to the set. Customarily, this is accomplished by maintaining a master configuration record in a stable storage device on the system, which, inter alia, identifies all devices that are configured for the set, and maintaining an identifying token or tokens on each device to identify it as part of a unique configuration set. The token is frequently based on information such as system serial number, device serial number, time-stamps, physical device characteristics (e.g. type, model, features and size), logical device identification number, set number, etc., though the token can be based on anything that will guarantee uniqueness, both on the system to which the devices are attached and among all sets for similar systems. During the booting up of the system, the system reads the master configuration record and utilizes it with the tokens to determine which devices are part of the system configuration.
Over time, the storage capacity of the computer system may need to be changed due to a hardware problem or the addition of new application or data to the system. In addition, the auxiliary storage devices configured as part of storage device sets may also need to be changed for a variety of reasons. When the composition of the storage device sets changes, the master configuration record and the identifying tokens must be updated for all configured members within a set. This is required when devices are added (so that new device is accepted as a valid member of the set), removed (so that old device is no longer accepted as part of the set), or replaced (so that the replaced device can never be mistaken for the replacement device in the future). Typically, in order to make a change in the master configuration records, the system dictates that all mass storage devices that are part of the system configuration must be accessible, i.e. present and operational. System availability needs, however, require that configuration updates and changes be allowed even if not all currently configured devices are available. Otherwise, the system will be unusable until the unavailable devices have been replaced or repaired.
Consequently, it would be desirable to provide a method for making a configuration change when not all members of a configured set are present or operational while guaranteeing the integrity of the set along with the data the set contains.